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Patiño-Ruiz MF, Anshari ZR, Gaastra B, Slotboom DJ, Poolman B. Chemiosmotic nutrient transport in synthetic cells powered by electrogenic antiport coupled to decarboxylation. Nat Commun 2024; 15:7976. [PMID: 39266519 PMCID: PMC11392934 DOI: 10.1038/s41467-024-52085-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2024] [Accepted: 08/27/2024] [Indexed: 09/14/2024] Open
Abstract
Cellular homeostasis depends on the supply of metabolic energy in the form of ATP and electrochemical ion gradients. The construction of synthetic cells requires a constant supply of energy to drive membrane transport and metabolism. Here, we provide synthetic cells with long-lasting metabolic energy in the form of an electrochemical proton gradient. Leveraging the L-malate decarboxylation pathway we generate a stable proton gradient and electrical potential in lipid vesicles by electrogenic L-malate/L-lactate exchange coupled to L-malate decarboxylation. By co-reconstitution with the transporters GltP and LacY, the synthetic cells maintain accumulation of L-glutamate and lactose over periods of hours, mimicking nutrient feeding in living cells. We couple the accumulation of lactose to a metabolic network for the generation of intermediates of the glycolytic and pentose phosphate pathways. This study underscores the potential of harnessing a proton motive force via a simple metabolic network, paving the way for the development of more complex synthetic systems.
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Affiliation(s)
- Miyer F Patiño-Ruiz
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands
| | - Zaid Ramdhan Anshari
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands
| | - Bauke Gaastra
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands
| | - Dirk J Slotboom
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands
| | - Bert Poolman
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands.
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2
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Reddy KD, Rasool B, Akher FB, Kutlešić N, Pant S, Boudker O. Evolutionary analysis reveals the origin of sodium coupling in glutamate transporters. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.12.03.569786. [PMID: 38106174 PMCID: PMC10723334 DOI: 10.1101/2023.12.03.569786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Secondary active membrane transporters harness the energy of ion gradients to concentrate their substrates. Homologous transporters evolved to couple transport to different ions in response to changing environments and needs. The bases of such diversification, and thus principles of ion coupling, are unexplored. Employing phylogenetics and ancestral protein reconstruction, we investigated sodium-coupled transport in prokaryotic glutamate transporters, a mechanism ubiquitous across life domains and critical to neurotransmitter recycling in humans. We found that the evolutionary transition from sodium-dependent to independent substrate binding to the transporter preceded changes in the coupling mechanism. Structural and functional experiments suggest that the transition entailed allosteric mutations, making sodium binding dispensable without affecting ion-binding sites. Allosteric tuning of transporters' energy landscapes might be a widespread route of their functional diversification.
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Affiliation(s)
- Krishna D. Reddy
- Dept. of Physiology & Biophysics, Weill Cornell Medical College, 1300 York Ave, New York, NY 10021, USA
| | - Burha Rasool
- Dept. of Physiology & Biophysics, Weill Cornell Medical College, 1300 York Ave, New York, NY 10021, USA
| | - Farideh Badichi Akher
- Dept. of Physiology & Biophysics, Weill Cornell Medical College, 1300 York Ave, New York, NY 10021, USA
| | - Nemanja Kutlešić
- Dept. of Physiology & Biophysics, Weill Cornell Medical College, 1300 York Ave, New York, NY 10021, USA
| | - Swati Pant
- Dept. of Biochemistry, Weill Cornell Medical College, 1300 York Ave, New York, NY 10021, USA
| | - Olga Boudker
- Dept. of Physiology & Biophysics, Weill Cornell Medical College, 1300 York Ave, New York, NY 10021, USA
- Howard Hughes Medical Institute, Weill Cornell Medical College, 1300 York Ave, New York, NY 10021, USA
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3
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Iovino L, Giusti V, Pischedda F, Giusto E, Plotegher N, Marte A, Battisti I, Di Iacovo A, Marku A, Piccoli G, Bandopadhyay R, Perego C, Bonifacino T, Bonanno G, Roseti C, Bossi E, Arrigoni G, Bubacco L, Greggio E, Hilfiker S, Civiero L. Trafficking of the glutamate transporter is impaired in LRRK2-related Parkinson's disease. Acta Neuropathol 2022; 144:81-106. [PMID: 35596783 PMCID: PMC9217889 DOI: 10.1007/s00401-022-02437-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Revised: 05/11/2022] [Accepted: 05/11/2022] [Indexed: 12/02/2022]
Abstract
The Excitatory Amino Acid Transporter 2 (EAAT2) accounts for 80% of brain glutamate clearance and is mainly expressed in astrocytic perisynaptic processes. EAAT2 function is finely regulated by endocytic events, recycling to the plasma membrane and degradation. Noteworthy, deficits in EAAT2 have been associated with neuronal excitotoxicity and neurodegeneration. In this study, we show that EAAT2 trafficking is impaired by the leucine-rich repeat kinase 2 (LRRK2) pathogenic variant G2019S, a common cause of late-onset familial Parkinson’s disease (PD). In LRRK2 G2019S human brains and experimental animal models, EAAT2 protein levels are significantly decreased, which is associated with elevated gliosis. The decreased expression of the transporter correlates with its reduced functionality in mouse LRRK2 G2019S purified astrocytic terminals and in Xenopus laevis oocytes expressing human LRRK2 G2019S. In LRRK2 G2019S knock-in mouse brain, the correct surface localization of the endogenous transporter is impaired, resulting in its interaction with a plethora of endo-vesicular proteins. Mechanistically, we report that pathogenic LRRK2 kinase activity delays the recycling of the transporter to the plasma membrane via Rabs inactivation, causing its intracellular re-localization and degradation. Taken together, our results demonstrate that pathogenic LRRK2 interferes with the physiology of EAAT2, pointing to extracellular glutamate overload as a possible contributor to neurodegeneration in PD.
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4
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Kovermann P, Engels M, Müller F, Fahlke C. Cellular Physiology and Pathophysiology of EAAT Anion Channels. Front Cell Neurosci 2022; 15:815279. [PMID: 35087380 PMCID: PMC8787812 DOI: 10.3389/fncel.2021.815279] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Accepted: 12/13/2021] [Indexed: 11/17/2022] Open
Abstract
Excitatory amino acid transporters (EAATs) optimize the temporal resolution and energy demand of mammalian excitatory synapses by quickly removing glutamate from the synaptic cleft into surrounding neuronal and glial cells and ensuring low resting glutamate concentrations. In addition to secondary active glutamate transport, EAATs also function as anion channels. The channel function of these transporters is conserved in all homologs ranging from archaebacteria to mammals; however, its physiological roles are insufficiently understood. There are five human EAATs, which differ in their glutamate transport rates. Until recently the high-capacity transporters EAAT1, EAAT2, and EAAT3 were believed to conduct only negligible anion currents, with no obvious function in cell physiology. In contrast, the low-capacity glutamate transporters EAAT4 and EAAT5 are thought to regulate neuronal signaling as glutamate-gated channels. In recent years, new experimental approaches and novel animal models, together with the discovery of a human genetic disease caused by gain-of-function mutations in EAAT anion channels have enabled identification of the first physiological and pathophysiological roles of EAAT anion channels.
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5
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Kovermann P, Kolobkova Y, Franzen A, Fahlke C. Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function. Epilepsia 2021; 63:388-401. [PMID: 34961934 DOI: 10.1111/epi.17154] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Revised: 12/09/2021] [Accepted: 12/09/2021] [Indexed: 11/28/2022]
Abstract
OBJECTIVE Mutations in the gene solute carrier family member 1A2 (SLC1A2) encoding the excitatory amino acid transporter 2 (EAAT2) are associated with severe forms of epileptic encephalopathy. EAAT2 is expressed in glial cells and presynaptic nerve terminals and represents the main l-glutamate uptake carrier in the mammalian brain. It does not only function as a secondary active glutamate transporter, but also as an anion channel. How naturally occurring mutations affect these two transport functions of EAAT2 and how such alterations cause epilepsy is insufficiently understood. METHODS Here we studied the functional consequences of three disease-associated mutations, which predict amino acid exchanges p.Gly82Arg (G82R), p.Leu85Pro (L85P), and p.Pro289Arg (P289R), by heterologous expression in mammalian cells, biochemistry, confocal imaging, and whole-cell patch-clamp recordings of EAAT2 l-glutamate transport and anion current. RESULTS G82R and L85P exchange amino acid residues contribute to the formation of the EAAT anion pore. They enlarge the pore diameter sufficiently to permit the passage of l-glutamate and thus function as l-glutamate efflux pathways. The mutation P289R decreases l-glutamate uptake, but increases anion currents despite a lower membrane expression. SIGNIFICANCE l-glutamate permeability of the EAAT anion pore is an unexpected functional consequence of naturally occurring single amino acid substitutions. l-glutamate efflux through mutant EAAT2 anion channels will cause glutamate excitotoxicity and neuronal hyperexcitability in affected patients. Antagonists that selectively suppress the EAAT anion channel function could serve as therapeutic agents in the future.
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Affiliation(s)
- Peter Kovermann
- Molekular- und Zellphysiologie (IBI-1) Forschungszentrum Jülich, Institute of Biological Information Processing, Jülich, Germany
| | - Yulia Kolobkova
- Molekular- und Zellphysiologie (IBI-1) Forschungszentrum Jülich, Institute of Biological Information Processing, Jülich, Germany
| | - Arne Franzen
- Molekular- und Zellphysiologie (IBI-1) Forschungszentrum Jülich, Institute of Biological Information Processing, Jülich, Germany
| | - Christoph Fahlke
- Molekular- und Zellphysiologie (IBI-1) Forschungszentrum Jülich, Institute of Biological Information Processing, Jülich, Germany
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Qu Q, Wang J, Li G, Chen R, Qu S. The Conformationally Sensitive Spatial Distance Between the TM3-4 Loop and Transmembrane Segment 7 in the Glutamate Transporter Revealed by Paired-Cysteine Mutagenesis. Front Cell Dev Biol 2021; 9:737629. [PMID: 34621751 PMCID: PMC8490817 DOI: 10.3389/fcell.2021.737629] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Accepted: 08/25/2021] [Indexed: 11/23/2022] Open
Abstract
Excitatory amino acid transporters can maintain extracellular glutamate concentrations lower than neurotoxic levels by transferring neurotransmitters from the synaptic cleft into surrounding glial cells and neurons. Previous work regarding the structural studies of GltPh, GltTK, excitatory amino acid transporter 1 (EAAT1), EAAT3 and alanine serine cysteine transporter 2 described the transport mechanism of the glutamate transporter in depth. However, much remains unknown about the role of the loop between transmembrane segment 3 and 4 during transport. To probe the function of this loop in the transport cycle, we engineered a pair of cysteine residues between the TM3-TM4 loop and TM7 in cysteine-less EAAT2. Here, we show that the oxidative cross-linking reagent CuPh inhibits transport activity of the paired mutant L149C/M414C, whereas DTT inhibits the effect of CuPh on transport activity of L149C/M414C. Additionally, we show that the effect of cross-linking in the mutant is due to the formation of the disulfide bond within the molecules of EAAT2. Further, L-glutamate or KCl protect, and D,L-threo-β-benzyloxy-aspartate (TBOA) increases, CuPh-induced inhibition in the L149C/M414 mutant, suggesting that the L149C and M414C cysteines are closer or farther away in the outward- or inward-facing conformations, respectively. Together, our findings provide evidence that the distance between TM3-TM4 loop and TM7 alter when substrates are transported.
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Affiliation(s)
- Qi Qu
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China.,Department of Neurobiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China.,Guangdong-Hong Kong-Macao Greater Bay Area Center for Brain Science and Brain-Inspired Intelligence, Guangzhou, China.,Key Laboratory of Mental Health of the Ministry of Education, Southern Medical University, Guangzhou, China
| | - Ji Wang
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China.,Guangdong-Hong Kong-Macao Greater Bay Area Center for Brain Science and Brain-Inspired Intelligence, Guangzhou, China.,Key Laboratory of Mental Health of the Ministry of Education, Southern Medical University, Guangzhou, China
| | - Guiping Li
- Department of Nuclear Medicine, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Rongqing Chen
- Department of Neurobiology, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
| | - Shaogang Qu
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China.,Guangdong-Hong Kong-Macao Greater Bay Area Center for Brain Science and Brain-Inspired Intelligence, Guangzhou, China.,Key Laboratory of Mental Health of the Ministry of Education, Southern Medical University, Guangzhou, China
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7
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Belo do Nascimento I, Damblon J, Ingelbrecht C, Goursaud S, Massart M, Dumont A, Desmet N, Hermans E. Pharmacological evidence for the concept of spare glutamate transporters. Neurochem Int 2021; 149:105142. [PMID: 34314789 DOI: 10.1016/j.neuint.2021.105142] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Revised: 07/09/2021] [Accepted: 07/22/2021] [Indexed: 01/30/2023]
Abstract
Through the efficient clearance of extracellular glutamate, high affinity astrocytic glutamate transporters constantly shape excitatory neurotransmission in terms of duration and spreading. Even though the glutamate transporter GLT-1 (also known as EAAT2/SLC1A2) is amongst the most abundant proteins in the mammalian brain, its density and activity are tightly regulated. In order to study the influence of changes in the expression of GLT-1 on glutamate uptake capacity, we have developed a model in HEK cells where the density of the transporter can be manipulated thanks to a tetracycline-inducible promoter. Exposing the cells to doxycycline concentration-dependently increased GLT-1 expression and substrate uptake velocity. However, beyond a certain level of induction, increasing the density of transporters at the cell surface failed to increase the maximal uptake. This suggested the progressive generation of a pool of spare transporters, a hypothesis that was further validated using the selective GLT-1 blocker WAY-213613 of which potency was influenced by the density of the transporters. The curve showing inhibition of uptake by increasing concentrations of WAY-213613 was indeed progressively rightward shifted when tested in cells where the transporter density was robustly induced. As largely documented in the context of cell-surface receptors, the existence of 'spare' glutamate transporters in the nervous tissue and particularly in astrocytes could impact on the consequences of physiological or pathological regulation of these transporters.
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Affiliation(s)
- Inês Belo do Nascimento
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200, Brussels, Belgium
| | - Jonathan Damblon
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200, Brussels, Belgium
| | - Caroline Ingelbrecht
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200, Brussels, Belgium
| | - Stéphanie Goursaud
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200, Brussels, Belgium
| | - Marion Massart
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200, Brussels, Belgium
| | - Amélie Dumont
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200, Brussels, Belgium
| | - Nathalie Desmet
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200, Brussels, Belgium
| | - Emmanuel Hermans
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200, Brussels, Belgium.
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8
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Rodríguez-Campuzano AG, Ortega A. Glutamate transporters: Critical components of glutamatergic transmission. Neuropharmacology 2021; 192:108602. [PMID: 33991564 DOI: 10.1016/j.neuropharm.2021.108602] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 04/09/2021] [Accepted: 04/27/2021] [Indexed: 02/06/2023]
Abstract
Glutamate is the major excitatory neurotransmitter in the vertebrate central nervous system. Once released, it binds to specific membrane receptors and transporters activating a wide variety of signal transduction cascades, as well as its removal from the synaptic cleft in order to avoid its extracellular accumulation and the overstimulation of extra-synaptic receptors that might result in neuronal death through a process known as excitotoxicity. Although neurodegenerative diseases are heterogenous in clinical phenotypes and genetic etiologies, a fundamental mechanism involved in neuronal degeneration is excitotoxicity. Glutamate homeostasis is critical for brain physiology and Glutamate transporters are key players in maintaining low extracellular Glutamate levels. Therefore, the characterization of Glutamate transporters has been an active area of glutamatergic research for the last 40 years. Transporter activity its regulated at different levels: transcriptional and translational control, transporter protein trafficking and membrane mobility, and through extensive post-translational modifications. The elucidation of these mechanisms has emerged as an important piece to shape our current understanding of glutamate actions in the nervous system.
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Affiliation(s)
- Ada G Rodríguez-Campuzano
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apartado Postal 14-740, Ciudad de México, 07000, Mexico
| | - Arturo Ortega
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apartado Postal 14-740, Ciudad de México, 07000, Mexico.
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Alleva C, Machtens JP, Kortzak D, Weyand I, Fahlke C. Molecular Basis of Coupled Transport and Anion Conduction in Excitatory Amino Acid Transporters. Neurochem Res 2021; 47:9-22. [PMID: 33587237 PMCID: PMC8763778 DOI: 10.1007/s11064-021-03252-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Revised: 01/18/2021] [Accepted: 01/19/2021] [Indexed: 12/15/2022]
Abstract
Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. After its release from presynaptic nerve terminals, glutamate is quickly removed from the synaptic cleft by excitatory amino acid transporters (EAATs) 1–5, a subfamily of glutamate transporters. The five proteins utilize a complex transport stoichiometry that couples glutamate transport to the symport of three Na+ ions and one H+ in exchange with one K+ to accumulate glutamate against up to 106-fold concentration gradients. They are also anion-selective channels that open and close during transitions along the glutamate transport cycle. EAATs belong to a larger family of secondary-active transporters, the SLC1 family, which also includes purely Na+- or H+-coupled prokaryotic transporters and Na+-dependent neutral amino acid exchangers. In recent years, molecular cloning, heterologous expression, cellular electrophysiology, fluorescence spectroscopy, structural approaches, and molecular simulations have uncovered the molecular mechanisms of coupled transport, substrate selectivity, and anion conduction in EAAT glutamate transporters. Here we review recent findings on EAAT transport mechanisms, with special emphasis on the highly conserved hairpin 2 gate, which has emerged as the central processing unit in many of these functions.
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Affiliation(s)
- Claudia Alleva
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1), Forschungszentrum Jülich, Jülich, Germany
| | - Jan-Philipp Machtens
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1), Forschungszentrum Jülich, Jülich, Germany.,Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany
| | - Daniel Kortzak
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1), Forschungszentrum Jülich, Jülich, Germany
| | - Ingo Weyand
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1), Forschungszentrum Jülich, Jülich, Germany
| | - Christoph Fahlke
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1), Forschungszentrum Jülich, Jülich, Germany.
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10
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Leng K, Li E, Eser R, Piergies A, Sit R, Tan M, Neff N, Li SH, Rodriguez RD, Suemoto CK, Leite REP, Ehrenberg AJ, Pasqualucci CA, Seeley WW, Spina S, Heinsen H, Grinberg LT, Kampmann M. Molecular characterization of selectively vulnerable neurons in Alzheimer's disease. Nat Neurosci 2021; 24:276-287. [PMID: 33432193 PMCID: PMC7854528 DOI: 10.1038/s41593-020-00764-7] [Citation(s) in RCA: 212] [Impact Index Per Article: 70.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2020] [Accepted: 11/20/2020] [Indexed: 01/29/2023]
Abstract
Alzheimer's disease (AD) is characterized by the selective vulnerability of specific neuronal populations, the molecular signatures of which are largely unknown. To identify and characterize selectively vulnerable neuronal populations, we used single-nucleus RNA sequencing to profile the caudal entorhinal cortex and the superior frontal gyrus-brain regions where neurofibrillary inclusions and neuronal loss occur early and late in AD, respectively-from postmortem brains spanning the progression of AD-type tau neurofibrillary pathology. We identified RORB as a marker of selectively vulnerable excitatory neurons in the entorhinal cortex and subsequently validated their depletion and selective susceptibility to neurofibrillary inclusions during disease progression using quantitative neuropathological methods. We also discovered an astrocyte subpopulation, likely representing reactive astrocytes, characterized by decreased expression of genes involved in homeostatic functions. Our characterization of selectively vulnerable neurons in AD paves the way for future mechanistic studies of selective vulnerability and potential therapeutic strategies for enhancing neuronal resilience.
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Affiliation(s)
- Kun Leng
- Institute for Neurodegenerative Disease, University of California, San Francisco, San Francisco, CA, USA
- Chan Zuckerberg Biohub, San Francisco, CA, USA
- Biomedical Sciences Graduate Program, University of California, San Francisco, San Francisco, CA, USA
- Medical Scientist Training Program, University of California, San Francisco, San Francisco, CA, USA
| | - Emmy Li
- Institute for Neurodegenerative Disease, University of California, San Francisco, San Francisco, CA, USA
- Chan Zuckerberg Biohub, San Francisco, CA, USA
- Biomedical Sciences Graduate Program, University of California, San Francisco, San Francisco, CA, USA
| | - Rana Eser
- Memory and Aging Center, Weill Institute for Neurosciences, Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Antonia Piergies
- Memory and Aging Center, Weill Institute for Neurosciences, Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Rene Sit
- Chan Zuckerberg Biohub, San Francisco, CA, USA
| | | | - Norma Neff
- Chan Zuckerberg Biohub, San Francisco, CA, USA
| | - Song Hua Li
- Memory and Aging Center, Weill Institute for Neurosciences, Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Roberta Diehl Rodriguez
- Department of Neurology, Universidade de São Paulo, Faculdade de Medicina, São Paulo, Brazil
| | - Claudia Kimie Suemoto
- Department of Pathology, Universidade de São Paulo, Faculdade de Medicina, São Paulo, Brazil
- Division of Geriatrics, Department of Clinical Medicine, Universidade de São Paulo, Faculdade de Medicina, São Paulo, Brazil
| | | | - Alexander J Ehrenberg
- Memory and Aging Center, Weill Institute for Neurosciences, Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Carlos A Pasqualucci
- Department of Pathology, Universidade de São Paulo, Faculdade de Medicina, São Paulo, Brazil
| | - William W Seeley
- Memory and Aging Center, Weill Institute for Neurosciences, Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
- Department of Pathology, University of California, San Francisco, San Francisco, CA, USA
| | - Salvatore Spina
- Memory and Aging Center, Weill Institute for Neurosciences, Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Helmut Heinsen
- Department of Pathology, Universidade de São Paulo, Faculdade de Medicina, São Paulo, Brazil
- Department of Psychiatry, University of Würzburg, Würzburg, Germany
| | - Lea T Grinberg
- Memory and Aging Center, Weill Institute for Neurosciences, Department of Neurology, University of California, San Francisco, San Francisco, CA, USA.
- Department of Pathology, Universidade de São Paulo, Faculdade de Medicina, São Paulo, Brazil.
- Global Brain Health Institute, University of California, San Francisco, San Francisco, CA, USA.
| | - Martin Kampmann
- Institute for Neurodegenerative Disease, University of California, San Francisco, San Francisco, CA, USA.
- Chan Zuckerberg Biohub, San Francisco, CA, USA.
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA, USA.
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11
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Chivukula AS, Suslova M, Kortzak D, Kovermann P, Fahlke C. Functional consequences of SLC1A3 mutations associated with episodic ataxia 6. Hum Mutat 2020; 41:1892-1905. [PMID: 32741053 DOI: 10.1002/humu.24089] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Revised: 07/09/2020] [Accepted: 07/27/2020] [Indexed: 11/09/2022]
Abstract
The episodic ataxias (EA) are a group of inherited neurological diseases characterized by paroxysmal cerebellar incoordination. There exist nine forms of episodic ataxia with distinct neurological symptoms and genetic origins. Episodic ataxia type 6 (EA6) differs from other EA forms in long attack duration, epilepsy and absent myokymia, nystagmus, and tinnitus. It has been described in seven families, and mutations in SLC1A3, the gene encoding the glial glutamate transporter EAAT1, were reported in each family. How these mutations affect EAAT1 expression, subcellular localization, and function, and how such alterations result in the complex neurological phenotype of EA6 is insufficiently understood. We here compare the functional consequences of all currently known mutations by heterologous expression in mammalian cells, biochemistry, confocal imaging, and whole-cell patch clamp recordings of EAAT1 transport and anion currents. We observed impairments of multiple EAAT1 properties ranging from changes in transport function, impaired trafficking to increased protein expression. Many mutations caused only slight changes illustrating how sensitively the cerebellum reacts on impaired EAAT1 functions.
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Affiliation(s)
- Aparna S Chivukula
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1) Forschungszentrum Jülich, Jülich, Germany
| | - Mariia Suslova
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1) Forschungszentrum Jülich, Jülich, Germany
| | - Daniel Kortzak
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1) Forschungszentrum Jülich, Jülich, Germany
| | - Peter Kovermann
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1) Forschungszentrum Jülich, Jülich, Germany
| | - Christoph Fahlke
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1) Forschungszentrum Jülich, Jülich, Germany
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12
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Kolen B, Kortzak D, Franzen A, Fahlke C. An amino-terminal point mutation increases EAAT2 anion currents without affecting glutamate transport rates. J Biol Chem 2020; 295:14936-14947. [PMID: 32820048 DOI: 10.1074/jbc.ra120.013704] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Revised: 08/03/2020] [Indexed: 12/16/2022] Open
Abstract
Excitatory amino acid transporters (EAATs) are prototypical dual function proteins that function as coupled glutamate/Na+/H+/K+ transporters and as anion-selective channels. Both transport functions are intimately intertwined at the structural level: Secondary active glutamate transport is based on elevator-like movements of the mobile transport domain across the membrane, and the lateral movement of this domain results in anion channel opening. This particular anion channel gating mechanism predicts the existence of mutant transporters with changed anion channel properties, but without alteration in glutamate transport. We here report that the L46P mutation in the human EAAT2 transporter fulfills this prediction. L46 is a pore-forming residue of the EAAT2 anion channels at the cytoplasmic entrance into the ion conduction pathway. In whole-cell patch clamp recordings, we observed larger macroscopic anion current amplitudes for L46P than for WT EAAT2. Rapid l-glutamate application under forward transport conditions demonstrated that L46P does not reduce the transport rate of individual transporters. In contrast, changes in selectivity made gluconate permeant in L46P EAAT2, and nonstationary noise analysis revealed slightly increased unitary current amplitudes in mutant EAAT2 anion channels. We used unitary current amplitudes and individual transport rates to quantify absolute open probabilities of EAAT2 anion channels from ratios of anion currents by glutamate uptake currents. This analysis revealed up to 7-fold increased absolute open probability of L46P EAAT2 anion channels. Our results reveal an important determinant of the diameter of EAAT2 anion pore and demonstrate the existence of anion channel gating processes outside the EAAT uptake cycle.
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Affiliation(s)
- Bettina Kolen
- Molekular- und Zellphysiologie (IBI-1), Institute of Biological Information Processing, Forschungszentrum Jülich, Jülich, Germany
| | - Daniel Kortzak
- Molekular- und Zellphysiologie (IBI-1), Institute of Biological Information Processing, Forschungszentrum Jülich, Jülich, Germany
| | - Arne Franzen
- Molekular- und Zellphysiologie (IBI-1), Institute of Biological Information Processing, Forschungszentrum Jülich, Jülich, Germany
| | - Christoph Fahlke
- Molekular- und Zellphysiologie (IBI-1), Institute of Biological Information Processing, Forschungszentrum Jülich, Jülich, Germany.
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13
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Solute carrier transporters: the metabolic gatekeepers of immune cells. Acta Pharm Sin B 2020; 10:61-78. [PMID: 31993307 PMCID: PMC6977534 DOI: 10.1016/j.apsb.2019.12.006] [Citation(s) in RCA: 111] [Impact Index Per Article: 27.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Revised: 09/29/2019] [Accepted: 10/31/2019] [Indexed: 02/06/2023] Open
Abstract
Solute carrier (SLC) transporters meditate many essential physiological functions, including nutrient uptake, ion influx/efflux, and waste disposal. In its protective role against tumors and infections, the mammalian immune system coordinates complex signals to support the proliferation, differentiation, and effector function of individual cell subsets. Recent research in this area has yielded surprising findings on the roles of solute carrier transporters, which were discovered to regulate lymphocyte signaling and control their differentiation, function, and fate by modulating diverse metabolic pathways and balanced levels of different metabolites. In this review, we present current information mainly on glucose transporters, amino-acid transporters, and metal ion transporters, which are critically important for mediating immune cell homeostasis in many different pathological conditions.
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Key Words
- 3-PG, 3-phosphoglyceric acid
- ABC, ATP-binding cassette
- AIF, apoptosis-inducing factor
- AP-1, activator protein 1
- ASCT2, alanine serine and cysteine transporter system 2
- ATP, adenosine triphosphate
- BCR, B cell receptor
- BMDMs, bone marrow-derived macrophages
- CD45R, a receptor-type protein tyrosine phosphatase
- CTL, cytotoxic T lymphocytes
- DC, dendritic cells
- EAATs, excitatory amino acid transporters
- ER, endoplasmic reticulum
- ERRα, estrogen related receptor alpha
- FFA, free fatty acids
- G-6-P, glucose 6-phosphate
- GLUT, glucose transporters
- GSH, glutathione
- Glucose
- Glutamine
- HIF-1α, hypoxia-inducible factor 1-alpha
- HIV-1, human immunodeficiency virus type 1
- Hk1, hexokinase-1
- IFNβ, interferon beta
- IFNγ, interferon gamma
- IKK, IκB kinase
- IKKβ, IκB kinase beta subunit
- IL, interleukin
- LDHA, lactate dehydrogenase A
- LPS, lipopolysaccharide
- Lymphocytes
- Lyn, tyrosine-protein kinase
- MAPK, mitogen-activated protein kinase
- MCT, monocarboxylate transporters
- MS, multiple sclerosis
- Metal ion
- NADPH, nicotinamide adenine dinucleotide phosphate
- NF-κB, nuclear factor kappa-light-chain-enhancer of activated B cells
- NO, nitric oxide
- NOD2, nucleotide-binding oligomerization domain containing 2
- PEG2, prostaglandin E2
- PI-3K/AKT, phosphatidylinositol-3-OH kinase/serine–threonine kinase
- PPP, pentose phosphate pathway
- Pfk, phosphofructokinase
- RA, rheumatoid arthritis
- RLR, RIG-I-like receptor
- ROS, reactive oxygen species
- SLC, solute carrier
- SLE, systemic lupus erythematosus
- SNAT, sodium-coupled neutral amino acid transporters
- STAT, signal transducers and activators of transcription
- Solute carrier
- TAMs, tumor-associated macrophages
- TCA, tricarboxylic acid
- TCR, T cell receptor
- TLR, toll-like receptor
- TNF, tumor necrosis factor
- TRPM7, transient receptor potential cation channel subfamily M member 7
- Teffs, effector T cells
- Th1/2/17, type 1/2/17 helper T cells
- Tregs, regulatory T cells
- VEGF, vascular endothelial growth factor
- ZIP, zrt/irt-like proteins
- iNOS, inducible nitric oxide synthase
- iTregs, induced regulatory T cells
- mTORC1, mammalian target of rapamycin complex 1
- α-KG, α-ketoglutaric acid
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14
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Malik AR, Willnow TE. Excitatory Amino Acid Transporters in Physiology and Disorders of the Central Nervous System. Int J Mol Sci 2019; 20:ijms20225671. [PMID: 31726793 PMCID: PMC6888459 DOI: 10.3390/ijms20225671] [Citation(s) in RCA: 88] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Revised: 11/07/2019] [Accepted: 11/11/2019] [Indexed: 12/12/2022] Open
Abstract
Excitatory amino acid transporters (EAATs) encompass a class of five transporters with distinct expression in neurons and glia of the central nervous system (CNS). EAATs are mainly recognized for their role in uptake of the amino acid glutamate, the major excitatory neurotransmitter. EAATs-mediated clearance of glutamate released by neurons is vital to maintain proper glutamatergic signalling and to prevent toxic accumulation of this amino acid in the extracellular space. In addition, some EAATs also act as chloride channels or mediate the uptake of cysteine, required to produce the reactive oxygen speciesscavenger glutathione. Given their central role in glutamate homeostasis in the brain, as well as their additional activities, it comes as no surprise that EAAT dysfunctions have been implicated in numerous acute or chronic diseases of the CNS, including ischemic stroke and epilepsy, cerebellar ataxias, amyotrophic lateral sclerosis, Alzheimer’s disease and Huntington’s disease. Here we review the studies in cellular and animal models, as well as in humans that highlight the roles of EAATs in the pathogenesis of these devastating disorders. We also discuss the mechanisms regulating EAATs expression and intracellular trafficking and new exciting possibilities to modulate EAATs and to provide neuroprotection in course of pathologies affecting the CNS.
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Affiliation(s)
- Anna R. Malik
- Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland
- Correspondence:
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15
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Glutamate transporters: a broad review of the most recent archaeal and human structures. Biochem Soc Trans 2019; 47:1197-1207. [PMID: 31383819 DOI: 10.1042/bst20190316] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 07/11/2019] [Accepted: 07/15/2019] [Indexed: 12/11/2022]
Abstract
Glutamate transporters play important roles in bacteria, archaea and eukaryotes. Their function in the mammalian central nervous system is essential for preventing excitotoxicity, and their dysregulation is implicated in many diseases, such as epilepsy and Alzheimer's. Elucidating their transport mechanism would further the understanding of these transporters and promote drug design as they provide compelling targets for understanding the pathophysiology of diseases and may have a direct role in the treatment of conditions involving glutamate excitotoxicity. This review outlines the insights into the transport cycle, uncoupled chloride conductance and modulation, as well as identifying areas that require further investigation.
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16
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Parkin GM, Udawela M, Gibbons A, Dean B. Glutamate transporters, EAAT1 and EAAT2, are potentially important in the pathophysiology and treatment of schizophrenia and affective disorders. World J Psychiatry 2018; 8:51-63. [PMID: 29988908 PMCID: PMC6033743 DOI: 10.5498/wjp.v8.i2.51] [Citation(s) in RCA: 77] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 05/15/2018] [Accepted: 06/09/2018] [Indexed: 02/05/2023] Open
Abstract
Glutamate is the predominant excitatory neurotransmitter in the human brain and it has been shown that prolonged activation of the glutamatergic system leads to nerve damage and cell death. Following release from the pre-synaptic neuron and synaptic transmission, glutamate is either taken up into the pre-synaptic neuron or neighbouring glia by transmembrane glutamate transporters. Excitatory amino acid transporter (EAAT) 1 and EAAT2 are Na+-dependant glutamate transporters expressed predominantly in glia cells of the central nervous system. As the most abundant glutamate transporters, their primary role is to modulate levels of glutamatergic excitability and prevent spill over of glutamate beyond the synapse. This role is facilitated through the binding and transportation of glutamate into astrocytes and microglia. The function of EAAT1 and EAAT2 is heavily regulated at the levels of gene expression, post-transcriptional splicing, glycosylation states and cell-surface trafficking of the protein. Both glutamatergic dysfunction and glial dysfunction have been proposed to be involved in psychiatric disorder. This review will present an overview of the roles that EAAT1 and EAAT2 play in modulating glutamatergic activity in the human brain, and mount an argument that these two transporters could be involved in the aetiologies of schizophrenia and affective disorders as well as represent potential drug targets for novel therapies for those disorders.
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Affiliation(s)
- Georgia M Parkin
- Molecular Psychiatry Laboratory, the Florey Institute of Neuroscience and Mental Health, Parkville VIC 3052, Australia
- CRC for Mental Health, Carlton VIC 3053, Australia
| | - Madhara Udawela
- Molecular Psychiatry Laboratory, the Florey Institute of Neuroscience and Mental Health, Parkville VIC 3052, Australia
- CRC for Mental Health, Carlton VIC 3053, Australia
| | - Andrew Gibbons
- Molecular Psychiatry Laboratory, the Florey Institute of Neuroscience and Mental Health, Parkville VIC 3052, Australia
| | - Brian Dean
- Molecular Psychiatry Laboratory, the Florey Institute of Neuroscience and Mental Health, Parkville VIC 3052, Australia
- CRC for Mental Health, Carlton VIC 3053, Australia
- Research Centre for Mental Health, the Faculty of Health, Arts and Design, Swinburne University, Hawthorne VIC 3122, Australia
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17
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Hashimoto M, Girardi E, Eichner R, Superti-Furga G. Detection of Chemical Engagement of Solute Carrier Proteins by a Cellular Thermal Shift Assay. ACS Chem Biol 2018; 13:1480-1486. [PMID: 29851333 PMCID: PMC6067815 DOI: 10.1021/acschembio.8b00270] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
Solute
carriers (SLCs) are transmembrane proteins that transport
various nutrients, metabolites, and drugs across cellular membranes.
Despite the relevance of SLCs to cell homeostasis, metabolism, and
disease states, for the majority of SLCs we lack experimental evidence
regarding the nature of the cognate ligands, whether endobiotic or
xenobiotic. Moreover, even for the roughly 20 SLCs for which inhibitors
have been characterized, engagement assays in cells are limited to
the accessibility of radiolabeled or fluorescent probes. The cellular
thermal shift assay (CETSA) has been introduced as a powerful method
to assess target engagement by monitoring ligand-induced changes in
the thermal stability of cellular proteins. We addressed the question
of whether CETSA could be modified to become routinely applicable
to membrane transporters such as SLCs. We used SLC16A1 (MCT1) and
SLC1A2 (EAAT2) as targets to establish robust conditions by which
chemical engagement of SLCs can be detected. Using immunoblotting,
we demonstrate that treatment with the SLC16A1 inhibitors AZD3965
and AR-C155858 stabilized endogenous SLC16A1 in HEK293 cell lysates
as well as intact cells. In addition, the high-affinity ligand of
SLC16A1, l-lactate, and the low-affinity ligand, formate,
resulted in strong and weak stabilization of SLC16A1, respectively.
Moreover, we observed stabilization of SLC1A2 upon treatment with
the selective inhibitor WAY-213613. We propose that the experimental
approach presented here should be generally and easily applicable
for monitoring the engagement of chemical ligands by SLCs in cellular
settings and thus assisting in their deorphanization.
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Affiliation(s)
- Mari Hashimoto
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, 1090 Vienna, Austria
| | - Enrico Girardi
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, 1090 Vienna, Austria
| | - Ruth Eichner
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, 1090 Vienna, Austria
| | - Giulio Superti-Furga
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, 1090 Vienna, Austria
- Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria
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18
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Arkhipova V, Guskov A, Slotboom DJ. Analysis of the quality of crystallographic data and the limitations of structural models. J Gen Physiol 2017; 149:1091-1103. [PMID: 29089418 PMCID: PMC5715909 DOI: 10.1085/jgp.201711852] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Accepted: 10/10/2017] [Indexed: 12/22/2022] Open
Abstract
Arkhipova et al. caution that the limitations of structural models be taken into account when interpreting crystallographic data. Crystal structures provide visual models of biological macromolecules, which are widely used to interpret data from functional studies and generate new mechanistic hypotheses. Because the quality of the collected x-ray diffraction data directly affects the reliability of the structural model, it is essential that the limitations of the models are carefully taken into account when making interpretations. Here we use the available crystal structures of members of the glutamate transporter family to illustrate the importance of inspecting the data that underlie the structural models. Crystal structures of glutamate transporters in multiple different conformations have been solved, but most structures were determined at relatively low resolution, with deposited models based on crystallographic data of moderate quality. We use these examples to demonstrate the extent to which mechanistic interpretations can be made safely.
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Affiliation(s)
- Valentina Arkhipova
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Groningen, Netherlands
| | - Albert Guskov
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Groningen, Netherlands
| | - Dirk-Jan Slotboom
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Groningen, Netherlands
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19
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Kovermann P, Hessel M, Kortzak D, Jen JC, Koch J, Fahlke C, Freilinger T. Impaired K + binding to glial glutamate transporter EAAT1 in migraine. Sci Rep 2017; 7:13913. [PMID: 29066757 PMCID: PMC5654970 DOI: 10.1038/s41598-017-14176-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Accepted: 10/06/2017] [Indexed: 12/28/2022] Open
Abstract
SLC1A3 encodes the glial glutamate transporter hEAAT1, which removes glutamate from the synaptic cleft via stoichiometrically coupled Na+-K+-H+-glutamate transport. In a young man with migraine with aura including hemiplegia, we identified a novel SLC1A3 mutation that predicts the substitution of a conserved threonine by proline at position 387 (T387P) in hEAAT1. To evaluate the functional effects of the novel variant, we expressed the wildtype or mutant hEAAT1 in mammalian cells and performed whole-cell patch clamp, fast substrate application, and biochemical analyses. T387P diminishes hEAAT1 glutamate uptake rates and reduces the number of hEAAT1 in the surface membrane. Whereas hEAAT1 anion currents display normal ligand and voltage dependence in cells internally dialyzed with Na+-based solution, no anion currents were observed with internal K+. Fast substrate application demonstrated that T387P abolishes K+-bound retranslocation. Our finding expands the phenotypic spectrum of genetic variation in SLC1A3 and highlights impaired K+ binding to hEAAT1 as a novel mechanism of glutamate transport dysfunction in human disease.
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Affiliation(s)
- Peter Kovermann
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, Jülich, Germany
| | - Margarita Hessel
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, Jülich, Germany
| | - Daniel Kortzak
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, Jülich, Germany
| | - Joanna C Jen
- Departments of Neurology and Neurobiology, UCLA School of Medicine, Los Angeles, USA
| | - Johannes Koch
- Department of Paediatrics, Salzburger Universitätsklinikum, Salzburg, Austria
| | - Christoph Fahlke
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, Jülich, Germany
| | - Tobias Freilinger
- Department of Neurology and Epileptology, Hertie-Institute for Clinical Brain Research (HIH), Tübingen, Germany.
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20
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Cheng MH, Torres-Salazar D, Gonzalez-Suarez AD, Amara SG, Bahar I. Substrate transport and anion permeation proceed through distinct pathways in glutamate transporters. eLife 2017; 6. [PMID: 28569666 PMCID: PMC5472439 DOI: 10.7554/elife.25850] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Accepted: 05/10/2017] [Indexed: 11/13/2022] Open
Abstract
Advances in structure-function analyses and computational biology have enabled a deeper understanding of how excitatory amino acid transporters (EAATs) mediate chloride permeation and substrate transport. However, the mechanism of structural coupling between these functions remains to be established. Using a combination of molecular modeling, substituted cysteine accessibility, electrophysiology and glutamate uptake assays, we identified a chloride-channeling conformer, iChS, transiently accessible as EAAT1 reconfigures from substrate/ion-loaded into a substrate-releasing conformer. Opening of the anion permeation path in this iChS is controlled by the elevator-like movement of the substrate-binding core, along with its wall that simultaneously lines the anion permeation path (global); and repacking of a cluster of hydrophobic residues near the extracellular vestibule (local). Moreover, our results demonstrate that stabilization of iChS by chemical modifications favors anion channeling at the expense of substrate transport, suggesting a mutually exclusive regulation mediated by the movement of the flexible wall lining the two regions.
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Affiliation(s)
- Mary Hongying Cheng
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, United States
| | - Delany Torres-Salazar
- Laboratory of Molecular and Cellular Neurobiology, National Institute of Mental Health, National Institutes of Health, Bethesda, United States
| | - Aneysis D Gonzalez-Suarez
- Laboratory of Molecular and Cellular Neurobiology, National Institute of Mental Health, National Institutes of Health, Bethesda, United States
| | - Susan G Amara
- Laboratory of Molecular and Cellular Neurobiology, National Institute of Mental Health, National Institutes of Health, Bethesda, United States
| | - Ivet Bahar
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, United States
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21
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Rose CR, Ziemens D, Untiet V, Fahlke C. Molecular and cellular physiology of sodium-dependent glutamate transporters. Brain Res Bull 2016; 136:3-16. [PMID: 28040508 DOI: 10.1016/j.brainresbull.2016.12.013] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 12/20/2016] [Accepted: 12/21/2016] [Indexed: 02/04/2023]
Abstract
Glutamate is the major excitatory transmitter in the vertebrate brain. After its release from presynaptic nerve terminals, it is rapidly taken up by high-affinity sodium-dependent plasma membrane transporters. While both neurons and glial cells express these excitatory amino acid transporters (EAATs), the majority of glutamate uptake is accomplished by astrocytes, which convert synaptically-released glutamate to glutamine or feed it into their own metabolism. Glutamate uptake by astrocytes not only shapes synaptic transmission by regulating the availability of glutamate to postsynaptic neuronal receptors, but also protects neurons from hyper-excitability and subsequent excitotoxic damage. In the present review, we provide an overview of the molecular and cellular characteristics of sodium-dependent glutamate transporters and their associated anion permeation pathways, with a focus on astrocytic glutamate transport. We summarize their functional properties and roles within tripartite synapses under physiological and pathophysiological conditions, exemplifying the intricate interactions and interrelationships between neurons and glial cells in the brain.
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Affiliation(s)
- Christine R Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, Germany.
| | - Daniel Ziemens
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, Germany
| | - Verena Untiet
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, Germany
| | - Christoph Fahlke
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, Germany
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22
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Characterisation of the DAACS Family Escherichia coli Glutamate/Aspartate-Proton Symporter GltP Using Computational, Chemical, Biochemical and Biophysical Methods. J Membr Biol 2016; 250:145-162. [DOI: 10.1007/s00232-016-9942-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2016] [Accepted: 12/09/2016] [Indexed: 10/20/2022]
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23
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Danbolt NC, Zhou Y, Furness DN, Holmseth S. Strategies for immunohistochemical protein localization using antibodies: What did we learn from neurotransmitter transporters in glial cells and neurons. Glia 2016; 64:2045-2064. [PMID: 27458697 DOI: 10.1002/glia.23027] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Revised: 06/19/2016] [Accepted: 06/21/2016] [Indexed: 12/11/2022]
Abstract
Immunocytochemistry and Western blotting are still major methods for protein localization, but they rely on the specificity of the antibodies. Validation of antibody specificity remains challenging mostly because ideal negative controls are often unavailable. Further, immunochemical labeling patterns are also influenced by a number of other factors such as postmortem changes, fixation procedures and blocking agents as well as the general assay conditions (e.g., buffers, temperature, etc.). Western blotting similarly depends on tissue collection and sample preparation as well as the electrophoretic separation, transfer to blotting membranes and the immunochemical probing of immobilized molecules. Publication of inaccurate information on protein distribution has downstream consequences for other researchers because the interpretation of physiological and pharmacological observations depends on information on where ion channels, receptors, enzymes or transporters are located. Despite numerous reports, some of which are strongly worded, erroneous localization data are being published. Here we describe the extent of the problem and illustrate the nature of the pitfalls with examples from studies of neurotransmitter transporters. We explain the importance of supplementing immunochemical observations with other measurements (e.g., mRNA levels and distribution, protein activity, mass spectrometry, electrophysiological recordings, etc.) and why quantitative considerations are integral parts of the quality control. Further, we propose a practical strategy for researchers who plan to embark on a localization study. We also share our thoughts about guidelines for quality control. GLIA 2016;64:2045-2064.
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Affiliation(s)
- Niels Christian Danbolt
- Neurotransporter Group, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.
| | - Yun Zhou
- Neurotransporter Group, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - David N Furness
- School of Life Sciences, Keele University, Keele, Staffs, United Kingdom
| | - Silvia Holmseth
- Neurotransporter Group, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
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24
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Bjørn-Yoshimoto WE, Underhill SM. The importance of the excitatory amino acid transporter 3 (EAAT3). Neurochem Int 2016; 98:4-18. [PMID: 27233497 DOI: 10.1016/j.neuint.2016.05.007] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 05/09/2016] [Accepted: 05/17/2016] [Indexed: 12/21/2022]
Abstract
The neuronal excitatory amino acid transporter 3 (EAAT3) is fairly ubiquitously expressed in the brain, though it does not necessarily maintain the same function everywhere. It is important in maintaining low local concentrations of glutamate, where its predominant post-synaptic localization can buffer nearby glutamate receptors and modulate excitatory neurotransmission and synaptic plasticity. It is also the main neuronal cysteine uptake system acting as the rate-limiting factor for the synthesis of glutathione, a potent antioxidant, in EAAT3 expressing neurons, while on GABAergic neurons, it is important in supplying glutamate as a precursor for GABA synthesis. Several diseases implicate EAAT3, and modulation of this transporter could prove a useful therapeutic approach. Regulation of EAAT3 could be targeted at several points for functional modulation, including the level of transcription, trafficking and direct pharmacological modulation, and indeed, compounds and experimental treatments have been identified that regulate EAAT3 function at different stages, which together with observations of EAAT3 regulation in patients is giving us insight into the endogenous function of this transporter, as well as the consequences of altered function. This review summarizes work done on elucidating the role and regulation of EAAT3.
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Affiliation(s)
- Walden E Bjørn-Yoshimoto
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100 København Ø, Denmark
| | - Suzanne M Underhill
- National Institute of Mental Health, National Institutes of Health, 35 Convent Drive Room 3A: 210 MSC3742, Bethesda, MD 20892-3742, USA.
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25
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Fahlke C, Kortzak D, Machtens JP. Molecular physiology of EAAT anion channels. Pflugers Arch 2015; 468:491-502. [PMID: 26687113 DOI: 10.1007/s00424-015-1768-3] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Revised: 11/24/2015] [Accepted: 11/26/2015] [Indexed: 12/25/2022]
Abstract
Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. After release from presynaptic nerve terminals, glutamate is quickly removed from the synaptic cleft by a family of five glutamate transporters, the so-called excitatory amino acid transporters (EAAT1-5). EAATs are prototypic members of the growing number of dual-function transport proteins: they are not only glutamate transporters, but also anion channels. Whereas the mechanisms underlying secondary active glutamate transport are well understood at the functional and at the structural level, mechanisms and cellular roles of EAAT anion conduction have remained elusive for many years. Recently, molecular dynamics simulations combined with simulation-guided mutagenesis and experimental analysis identified a novel anion-conducting conformation, which accounts for all experimental data on EAAT anion currents reported so far. We here review recent findings on how EAATs accommodate a transporter and a channel in one single protein.
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Affiliation(s)
- Christoph Fahlke
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, 52425, Jülich, Germany.
| | - Daniel Kortzak
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, 52425, Jülich, Germany
| | - Jan-Philipp Machtens
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, 52425, Jülich, Germany
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Hausmann R, Kless A, Schmalzing G. Key sites for P2X receptor function and multimerization: overview of mutagenesis studies on a structural basis. Curr Med Chem 2015; 22:799-818. [PMID: 25439586 PMCID: PMC4460280 DOI: 10.2174/0929867322666141128163215] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Revised: 10/20/2014] [Accepted: 11/27/2014] [Indexed: 02/07/2023]
Abstract
P2X receptors constitute a seven-member family (P2X1-7) of extracellular ATP-gated cation
channels of widespread expression. Because P2X receptors have been implicated in neurological, inflammatory
and cardiovascular diseases, they constitute promising drug targets. Since the first P2X cDNA sequences
became available in 1994, numerous site-directed mutagenesis studies have been conducted to disclose
key sites of P2X receptor function and oligomerization. The publication of the 3-Å crystal structures of the zebrafish
P2X4 (zfP2X4) receptor in the homotrimeric apo-closed and ATP-bound open states in 2009 and 2012, respectively, has
ushered a new era by allowing for the interpretation of the wealth of molecular data in terms of specific three-dimensional
models and by paving the way for designing more-decisive experiments. Thanks to these structures, the last five years
have provided invaluable insight into our understanding of the structure and function of the P2X receptor class of ligandgated
ion channels. In this review, we provide an overview of mutagenesis studies of the pre- and post-crystal structure
eras that identified amino acid residues of key importance for ligand binding, channel gating, ion flow, formation of the
pore and the channel gate, and desensitization. In addition, the sites that are involved in the trimerization of P2X receptors
are reviewed based on mutagenesis studies and interface contacts that were predicted by the zfP2X4 crystal structures.
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Affiliation(s)
| | | | - Gunther Schmalzing
- Department of Molecular Pharmacology, Medical Faculty of the RWTH Aachen University, Wendlingweg 2, D-52074 Aachen, Germany.
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Takahashi K, Foster JB, Lin CLG. Glutamate transporter EAAT2: regulation, function, and potential as a therapeutic target for neurological and psychiatric disease. Cell Mol Life Sci 2015; 72:3489-506. [PMID: 26033496 PMCID: PMC11113985 DOI: 10.1007/s00018-015-1937-8] [Citation(s) in RCA: 119] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Revised: 05/22/2015] [Accepted: 05/26/2015] [Indexed: 12/12/2022]
Abstract
Glutamate is the predominant excitatory neurotransmitter in the central nervous system. Excitatory amino acid transporter 2 (EAAT2) is primarily responsible for clearance of extracellular glutamate to prevent neuronal excitotoxicity and hyperexcitability. EAAT2 plays a critical role in regulation of synaptic activity and plasticity. In addition, EAAT2 has been implicated in the pathogenesis of many central nervous system disorders. In this review, we summarize current understanding of EAAT2, including structure, pharmacology, physiology, and functions, as well as disease relevancy, such as in stroke, Parkinson's disease, epilepsy, amyotrophic lateral sclerosis, Alzheimer's disease, major depressive disorder, and addiction. A large number of studies have demonstrated that up-regulation of EAAT2 protein provides significant beneficial effects in many disease models suggesting EAAT2 activation is a promising therapeutic approach. Several EAAT2 activators have been identified. Further understanding of EAAT2 regulatory mechanisms could improve development of drug-like compounds that spatiotemporally regulate EAAT2.
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Affiliation(s)
- Kou Takahashi
- Department of Neuroscience, The Ohio State University, 333 West 10th Avenue, Columbus, OH 43210 USA
| | - Joshua B. Foster
- Department of Neuroscience, The Ohio State University, 333 West 10th Avenue, Columbus, OH 43210 USA
| | - Chien-Liang Glenn Lin
- Department of Neuroscience, The Ohio State University, 333 West 10th Avenue, Columbus, OH 43210 USA
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Torres-Salazar D, Jiang J, Divito CB, Garcia-Olivares J, Amara SG. A Mutation in Transmembrane Domain 7 (TM7) of Excitatory Amino Acid Transporters Disrupts the Substrate-dependent Gating of the Intrinsic Anion Conductance and Drives the Channel into a Constitutively Open State. J Biol Chem 2015. [PMID: 26203187 DOI: 10.1074/jbc.m115.660860] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In the mammalian central nervous system, excitatory amino acid transporters (EAATs) are responsible for the clearance of glutamate after synaptic release. This energetically demanding activity is crucial for precise neuronal communication and for maintaining extracellular glutamate concentrations below neurotoxic levels. In addition to their ability to recapture glutamate from the extracellular space, EAATs exhibit a sodium- and glutamate-gated anion conductance. Here we show that substitution of a conserved positively charged residue (Arg-388, hEAAT1) in transmembrane domain 7 with a negatively charged amino acid eliminates the ability of glutamate to further activate the anion conductance. When expressed in oocytes, R388D or R388E mutants show large anion currents that display no further increase in amplitude after application of saturating concentrations of Na(+) and glutamate. They also show a substantially reduced transport activity. The mutant transporters appear to exist preferentially in a sodium- and glutamate-independent constitutive open channel state that rarely transitions to complete the transport cycle. In addition, the accessibility of cytoplasmic residues to membrane-permeant modifying reagents supports the idea that this substrate-independent open state correlates with an intermediate outward facing conformation of the transporter. Our data provide additional insights into the mechanism by which substrates gate the anion conductance in EAATs and suggest that in EAAT1, Arg-388 is a critical element for the structural coupling between the substrate translocation and the gating mechanisms of the EAAT-associated anion channel.
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Affiliation(s)
| | - Jie Jiang
- the Department of Neurobiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
| | - Christopher B Divito
- the Department of Neurobiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
| | | | - Susan G Amara
- From the National Institute of Mental Health, Bethesda, Maryland 20892 and the Department of Neurobiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
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29
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Afshari P, Myles-Worsley M, Cohen OS, Tiobech J, Faraone SV, Byerley W, Middleton FA. Characterization of a Novel Mutation in SLC1A1 Associated with Schizophrenia. MOLECULAR NEUROPSYCHIATRY 2015; 1:125-44. [PMID: 26380821 DOI: 10.1159/000433599] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 05/20/2015] [Indexed: 01/25/2023]
Abstract
We have recently described a hemi-deletion on chromosome 9p24.2 at the SLC1A1 gene locus and its co-segregation with schizophrenia in an extended Palauan pedigree. This finding represents a point of convergence for several pathophysiological models of schizophrenia. The present report sought to characterize the biological consequences of this hemi-deletion. Dual luciferase assays demonstrated that the partially deleted allele (lacking exon 1 and the native promoter) can drive expression of a 5'-truncated SLC1A1 using sequence upstream of exon 2 as a surrogate promoter. However, confocal microscopy and electrophysiological recordings demonstrate that the 5'-truncated SLC1A1 lacks normal membrane localization and glutamate transport ability. To identify downstream consequences of the hemi-deletion, we first used a themed qRT-PCR array to compare expression of 84 GABA and glutamate genes in RNA from peripheral blood leukocytes in deletion carriers (n = 11) versus noncarriers (n = 8) as well as deletion carriers with psychosis (n = 5) versus those without (n = 3). Then, targeted RNA-Seq (TREx) was used to quantify expression of 375 genes associated with neuropsychiatric disorders in HEK293 cells subjected to either knockdown of SLC1A1 or overexpression of full-length or 5'-truncated SLC1A1. Expression changes of several genes strongly implicated in schizophrenia pathophysiology were detected (e.g. SLC1A2, SLC1A3, SLC1A6, SLC7A11, GRIN2A, GRIA1 and DLX1).
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Affiliation(s)
- Parisa Afshari
- Departments of Neuroscience and Physiology, SUNY Upstate Medical University, Syracuse, N.Y., USA
| | - Marina Myles-Worsley
- Departments of Psychiatry and Behavioral Sciences, SUNY Upstate Medical University, Syracuse, N.Y., USA
| | - Ori S Cohen
- Departments of Psychiatry and Behavioral Sciences, SUNY Upstate Medical University, Syracuse, N.Y., USA
| | | | - Stephen V Faraone
- Departments of Neuroscience and Physiology, SUNY Upstate Medical University, Syracuse, N.Y., USA; Departments of Psychiatry and Behavioral Sciences, SUNY Upstate Medical University, Syracuse, N.Y., USA
| | - William Byerley
- Department of Psychiatry, University of California at San Francisco, San Francisco, Calif., USA
| | - Frank A Middleton
- Departments of Neuroscience and Physiology, SUNY Upstate Medical University, Syracuse, N.Y., USA; Departments of Psychiatry and Behavioral Sciences, SUNY Upstate Medical University, Syracuse, N.Y., USA; Departments of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, N.Y., USA
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Rao P, Saternos H, Goodwani S, Sari Y. Effects of ceftriaxone on GLT1 isoforms, xCT and associated signaling pathways in P rats exposed to ethanol. Psychopharmacology (Berl) 2015; 232:2333-42. [PMID: 25619881 PMCID: PMC4465848 DOI: 10.1007/s00213-015-3868-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Accepted: 01/11/2015] [Indexed: 02/07/2023]
Abstract
RATIONALE Several studies have demonstrated a correlation between extracellular glutamate concentration in the mesolimbic reward pathway and alcohol craving. Extracellular glutamate concentration is regulated by several glutamate transporters. Glial glutamate transporter 1 (GLT1) is one of them that regulates the majority of extracellular glutamate concentration. In addition, cystine/glutamate antiporter (xCT) is another transporter that regulates extracellular glutamate. OBJECTIVES We focus in this study to determine the effects of ceftriaxone, β-lactam antibiotic, on glial proteins such as GLT1 isoforms, xCT, glutamate aspartate transporter (GLAST), and several associated signaling pathways as well as ethanol intake in P rats. Additionally, to examine the onset of signaling pathways associated with GLT1 upregulation following ceftriaxone treatment, we tested 2- versus 5-day daily dosing of ceftriaxone. RESULTS Ceftriaxone treatment (100 mg/kg), 2 and 5 days, resulted in about five fold reduction in ethanol intake by P rats. The reduction in ethanol intake was associated with significantly enhanced expression of GLT1, GLT1a, GLT1b, and xCT in the nucleus accumbens (NAc) and prefrontal cortex (PFC) of 5-day ceftriaxone-treated P rats. Two-day-treated P rats showed marked changes in expression of these glutamate transporters in the PFC but not in the NAc. Importantly, ceftriaxone-treated P rats (2 and 5 days) demonstrated enhanced phosphorylation of Akt and nuclear translocation of nuclear factor kappaB (NFκB) in the NAc and PFC compared to control animals. CONCLUSIONS These findings demonstrate that ceftriaxone treatment induced upregulation of GLT1, GLT1 isoforms, and xCT in association with activation of the Akt-NFκB signaling pathway.
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Affiliation(s)
- P.S.S. Rao
- University of Toledo, College of Pharmacy and Pharmaceutical Sciences, Department of Pharmacology, Toledo, OH
| | - Hannah Saternos
- University of Toledo, College of Pharmacy and Pharmaceutical Sciences, Department of Pharmacology, Toledo, OH
| | - Sunil Goodwani
- University of Toledo, College of Pharmacy and Pharmaceutical Sciences, Department of Pharmacology, Toledo, OH
| | - Youssef Sari
- Department of Pharmacology, College of Pharmacy and Pharmaceutical Sciences, University of Toledo, Health Science Campus, 3000 Arlington Avenue, HEB282G, Toledo, OH, 43614, USA.
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Differential regulation of two isoforms of the glial glutamate transporter EAAT2 by DLG1 and CaMKII. J Neurosci 2015; 35:5260-70. [PMID: 25834051 DOI: 10.1523/jneurosci.4365-14.2015] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The gene for EAAT2, the major astrocytic glutamate transporter, generates two carrier isoforms (EAAT2a and EAAT2b) that vary at their C termini as a consequence of alternative RNA splicing. The EAAT2b cytoplasmic C terminus contains a postsynaptic density-95/Discs large/zona occludens-1 (PDZ) ligand, which is absent in EAAT2a. To understand how the distinct C termini might affect transporter trafficking and surface localization, we generated Madin-Darby canine kidney (MDCK) cells that stably express EGFP-EAAT2a or EGFP-EAAT2b and found robust basolateral membrane expression of the EAAT2b isoform. In contrast, EAAT2a displayed a predominant distribution within intracellular vesicle compartments, constitutively cycling to and from the membrane. Addition of the PDZ ligand to EAAT2a as well as its deletion from EAAT2b confirmed the importance of the motif for cell-surface localization. Using EAAT2 constructs with an extracellular biotin acceptor tag to directly assess surface proteins, we observed significant PDZ ligand-dependent EAAT2b surface expression in cultured astrocytes, consistent with observations in cell lines. Discs large homolog 1 (DLG1; SAP97), a PDZ protein prominent in both astrocytes and MDCK cells, colocalized and coimmunoprecipitated with EAAT2b. shRNA knockdown of DLG1 expression decreased surface EAAT2b in both MDCK cells and cultured astrocytes, suggesting that the DLG scaffolding protein stabilizes EAAT2b at the surface. DLG1 can be phosphorylated by Ca(2+)/calmodulin-dependent protein kinase (CaMKII), resulting in disruption of its PDZ-mediated interaction. In murine astrocytes and acute brain slices, activation of CaMKII decreases EAAT2b surface expression but does not alter the distribution of EAAT2a. These data indicate that the surface expression and function of EAAT2b can be rapidly modulated through the disruption of its interaction with DLG1 by CaMKII activation.
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Stolz M, Klapperstück M, Kendzierski T, Detro-Dassen S, Panning A, Schmalzing G, Markwardt F. Homodimeric anoctamin-1, but not homodimeric anoctamin-6, is activated by calcium increases mediated by the P2Y1 and P2X7 receptors. Pflugers Arch 2015; 467:2121-40. [PMID: 25592660 DOI: 10.1007/s00424-015-1687-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 12/23/2014] [Accepted: 01/06/2015] [Indexed: 01/14/2023]
Abstract
The P2X7 receptor (P2X7R) is a ligand-gated ion channel that conducts Na(+), K(+), and Ca(2+) when activated by extracellular ATP. In various cell types, such as secretory epithelia, the P2X7R is co-expressed with Ca(2+)-dependent Cl(-) channels of the TMEM16/anoctamin family. Here, we studied whether the P2X7R and TMEM16A/anoctamin-1 (Ano1) or TMEM16F/anoctamin-6 (Ano6) interact functionally and physically, using oocytes of Xenopus laevis and Ambystoma mexicanum (Axolotl) for heterologous expression. As a control, we co-expressed anoctamin-1 with the P2Y1 receptor (P2Y1R), which induces the release of Ca(2+) from intracellular stores via activating phospholipase C through coupling to Gαq. We found that co-expression of anoctamin-1 with the P2Y1R resulted in a small transient increase in Cl(-) conductance in response to ATP. Co-expression of anoctamin-1 with the P2X7R resulted in a large sustained increase in Cl(-) conductance via Ca(2+) influx through the ATP-opened P2X7R in Xenopus and in Axolotl oocytes, which lack endogenous Ca(2+)-dependent Cl(-) channels. P2Y1R- or P2X7R-mediated stimulation of Ano1 was primarily functional, as demonstrated by the absence of a physically stable interaction between Ano1 and the P2X7R. In the pancreatic cell line AsPC-1, we found the same functional Ca(2+)-dependent interaction of P2X7R and Ano1. The P2X7R-mediated sustained activation of Ano1 may be physiologically relevant to the time course of stimulus-secretion coupling in secretory epithelia. No such increase in Cl(-) conductance could be elicited by activating the P2X7 receptor in either Xenopus oocytes or Axolotl oocytes co-expressing Ano6. The lack of function of Ano6 can, at least in part, be explained by its poor cell-surface expression, resulting from a relatively inefficient exit of the homodimeric Ano6 from the endoplasmic reticulum.
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Affiliation(s)
- Michaela Stolz
- Molecular Pharmacology, RWTH Aachen University, Wendlingweg 2, D-52074, Aachen, Germany
| | - Manuela Klapperstück
- Julius-Bernstein-Institute for Physiology, Martin-Luther-University Halle-Wittenberg, Magdeburger Str. 6, D-06097, Halle/Saale, Germany
| | - Thomas Kendzierski
- Julius-Bernstein-Institute for Physiology, Martin-Luther-University Halle-Wittenberg, Magdeburger Str. 6, D-06097, Halle/Saale, Germany
| | - Silvia Detro-Dassen
- Molecular Pharmacology, RWTH Aachen University, Wendlingweg 2, D-52074, Aachen, Germany
| | - Anna Panning
- Molecular Pharmacology, RWTH Aachen University, Wendlingweg 2, D-52074, Aachen, Germany
| | - Günther Schmalzing
- Molecular Pharmacology, RWTH Aachen University, Wendlingweg 2, D-52074, Aachen, Germany
| | - Fritz Markwardt
- Julius-Bernstein-Institute for Physiology, Martin-Luther-University Halle-Wittenberg, Magdeburger Str. 6, D-06097, Halle/Saale, Germany.
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Karki P, Smith K, Johnson J, Aschner M, Lee E. Role of transcription factor yin yang 1 in manganese-induced reduction of astrocytic glutamate transporters: Putative mechanism for manganese-induced neurotoxicity. Neurochem Int 2014; 88:53-9. [PMID: 25128239 DOI: 10.1016/j.neuint.2014.08.002] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2014] [Revised: 07/31/2014] [Accepted: 08/05/2014] [Indexed: 10/24/2022]
Abstract
Astrocytes are the most abundant non-neuronal glial cells in the brain. Once relegated to a mere supportive role for neurons, contemporary dogmas ascribe multiple active roles for these cells in central nervous system (CNS) function, including maintenance of optimal glutamate levels in synapses. Regulation of glutamate levels in the synaptic cleft is crucial for preventing excitotoxic neuronal injury. Glutamate levels are regulated predominantly by two astrocytic glutamate transporters, glutamate transporter 1 (GLT-1) and glutamate aspartate transporter (GLAST). Indeed, the dysregulation of these transporters has been linked to several neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD) and Parkinson's disease (PD), as well as manganism, which is caused by overexposure to the trace metal, manganese (Mn). Although Mn is an essential trace element, its excessive accumulation in the brain as a result of chronic occupational or environmental exposures induces a neurological disorder referred to as manganism, which shares common pathological features with Parkinsonism. Mn decreases the expression and function of both GLAST and GLT-1. Astrocytes are commonly targeted by Mn, and thus reduction in astrocytic glutamate transporter function represents a critical mechanism of Mn-induced neurotoxicity. In this review, we will discuss the role of astrocytic glutamate transporters in neurodegenerative diseases and Mn-induced neurotoxicity.
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Affiliation(s)
- Pratap Karki
- Department of Physiology, Meharry Medical College, Nashville, TN 37208, United States
| | - Keisha Smith
- Department of Physiology, Meharry Medical College, Nashville, TN 37208, United States
| | - James Johnson
- Department of Physiology, Meharry Medical College, Nashville, TN 37208, United States
| | - Michael Aschner
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, United States
| | - Eunsook Lee
- Department of Physiology, Meharry Medical College, Nashville, TN 37208, United States.
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Verdon G, Oh S, Serio RN, Boudker O. Coupled ion binding and structural transitions along the transport cycle of glutamate transporters. eLife 2014; 3:e02283. [PMID: 24842876 PMCID: PMC4051121 DOI: 10.7554/elife.02283] [Citation(s) in RCA: 84] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Membrane transporters that clear the neurotransmitter glutamate from synapses are driven by symport of sodium ions and counter-transport of a potassium ion. Previous crystal structures of a homologous archaeal sodium and aspartate symporter showed that a dedicated transport domain carries the substrate and ions across the membrane. Here, we report new crystal structures of this homologue in ligand-free and ions-only bound outward- and inward-facing conformations. We show that after ligand release, the apo transport domain adopts a compact and occluded conformation that can traverse the membrane, completing the transport cycle. Sodium binding primes the transport domain to accept its substrate and triggers extracellular gate opening, which prevents inward domain translocation until substrate binding takes place. Furthermore, we describe a new cation-binding site ideally suited to bind a counter-transported ion. We suggest that potassium binding at this site stabilizes the translocation-competent conformation of the unloaded transport domain in mammalian homologues. DOI:http://dx.doi.org/10.7554/eLife.02283.001 Molecules of glutamate can carry messages between cells in the brain, and these signals are essential for thought and memory. Glutamate molecules can also act as signals to build new connections between brain cells and to prune away unnecessary ones. However, too much glutamate outside of the cells kills the brain tissue and can lead to devastating brain diseases. In a healthy brain, special pumps called glutamate transporters move these molecules back into the brain cells, where they can be stored safely. However, when brain cells are damaged—by, for example, a stroke or an injury,—the glutamate stored inside spills out, killing the surrounding cells. This leads to a cascade of dying cells and leaking glutamate, which causes even more damage and slows the recovery. Glutamate transporters ensure that there are more glutamate molecules inside cells than outside. However, it requires energy to maintain this gradient in the concentration of glutamate molecules. The transporters get this energy by moving three sodium ions into the cell with each glutamate molecule, and moving one potassium ion out of the cell. However, it is not clear how these transporters ensure that they move the glutamate molecules and the sodium ions at the same time. Now, Verdon, Oh et al. have uncovered the 3D structure of a glutamate transporter homologue at each step of the transport process. These structures reveal that, on the outside of the cell membrane, sodium ions attach to the so-called ‘transporter domain’ and make it better able to bind glutamate. The transporter domain then carries the sodium ions and glutamate through the cell membrane and releases them into the cell. Verdon, Oh et al. suggest that a potassium ion then binds to the empty transport domain, stabilizing it into a more compact shape that easily makes the return trip to the outside of the cell. Most experiments on glutamate transporters, including the work of Verdon, Oh et al., are carried out on model proteins taken from bacteria. An important challenge for the future will be to obtain structural information on human glutamate transporters, as these could be therapeutic targets for the treatment of various neurological conditions. DOI:http://dx.doi.org/10.7554/eLife.02283.002
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Affiliation(s)
- Grégory Verdon
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, United States
| | - SeCheol Oh
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, United States
| | - Ryan N Serio
- Department of Pharmacology, Weill Cornell Medical College, New York, United States
| | - Olga Boudker
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, United States
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35
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ClC-1 and ClC-2 form hetero-dimeric channels with novel protopore functions. Pflugers Arch 2014; 466:2191-204. [DOI: 10.1007/s00424-014-1490-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Accepted: 02/19/2014] [Indexed: 10/25/2022]
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36
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Boudker O, Akyuz N. Dance Lessons for Proteins: The Dynamics and Thermodynamics of a Sodium/Aspartate Symporter. SPRINGER SERIES IN BIOPHYSICS 2014. [DOI: 10.1007/978-3-642-53839-1_1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/08/2022]
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37
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Characterization of SLCO5A1/OATP5A1, a solute carrier transport protein with non-classical function. PLoS One 2013; 8:e83257. [PMID: 24376674 PMCID: PMC3869781 DOI: 10.1371/journal.pone.0083257] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Accepted: 11/01/2013] [Indexed: 12/14/2022] Open
Abstract
Organic anion transporting polypeptides (OATP/SLCO) have been identified to mediate the uptake of a broad range of mainly amphipathic molecules. Human OATP5A1 was found to be expressed in the epithelium of many cancerous and non-cancerous tissues throughout the body but protein characterization and functional analysis have not yet been performed. This study focused on the biochemical characterization of OATP5A1 using Xenopus laevis oocytes and Flp-In T-REx-HeLa cells providing evidence regarding a possible OATP5A1 function. SLCO5A1 is highly expressed in mature dendritic cells compared to immature dendritic cells (∼6.5-fold) and SLCO5A1 expression correlates with the differentiation status of primary blood cells. A core- and complex- N-glycosylated polypeptide monomer of ∼105 kDa and ∼130 kDa could be localized in intracellular membranes and on the plasma membrane, respectively. Inducible expression of SLCO5A1 in HeLa cells led to an inhibitory effect of ∼20% after 96 h on cell proliferation. Gene expression profiling with these cells identified immunologically relevant genes (e.g. CCL20) and genes implicated in developmental processes (e.g. TGM2). A single nucleotide polymorphism leading to the exchange of amino acid 33 (L→F) revealed no differences regarding protein expression and function. In conclusion, we provide evidence that OATP5A1 might be a non-classical OATP family member which is involved in biological processes that require the reorganization of the cell shape, such as differentiation and migration.
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Abstract
L-Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system and plays important roles in a wide variety of brain functions, but it is also a key player in the pathogenesis of many neurological disorders. The control of glutamate concentrations is critical to the normal functioning of the central nervous system, and in this review we discuss how glutamate transporters regulate glutamate concentrations to maintain dynamic signaling mechanisms between neurons. In 2004, the crystal structure of a prokaryotic homolog of the mammalian glutamate transporter family of proteins was crystallized and its structure determined. This has paved the way for a better understanding of the structural basis for glutamate transporter function. In this review we provide a broad perspective of this field of research, but focus primarily on the more recent studies with a particular emphasis on how our understanding of the structure of glutamate transporters has generated new insights.
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39
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Alexander SPH, Benson HE, Faccenda E, Pawson AJ, Sharman JL, Spedding M, Peters JA, Harmar AJ. The Concise Guide to PHARMACOLOGY 2013/14: transporters. Br J Pharmacol 2013; 170:1706-96. [PMID: 24528242 PMCID: PMC3892292 DOI: 10.1111/bph.12450] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. Transporters are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.
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Affiliation(s)
- Stephen PH Alexander
- School of Life Sciences, University of Nottingham Medical SchoolNottingham, NG7 2UH, UK
| | - Helen E Benson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Elena Faccenda
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Adam J Pawson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Joanna L Sharman
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | | | - John A Peters
- Neuroscience Division, Medical Education Institute, Ninewells Hospital and Medical School, University of DundeeDundee, DD1 9SY, UK
| | - Anthony J Harmar
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
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40
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Rojas R, Nishidomi S, Nepomuceno R, Oshiro E, de Cassia Café Ferreira R. Glutamate transport and xanthan gum production in the plant pathogen Xanthomonas axonopodis pv. citri. World J Microbiol Biotechnol 2013; 29:2173-80. [PMID: 23719672 DOI: 10.1007/s11274-013-1383-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Accepted: 05/20/2013] [Indexed: 11/28/2022]
Abstract
L-glutamate plays a central role in nitrogen metabolism in all living organisms. In the genus Xanthomonas, the nitrogen nutrition is an important factor involved in the xanthan gum production, an important exopolysaccharide with various industrial and biotechnological applications. In this report, we demonstrate that the use of L-glutamate by the phytopathogen Xanthomonas axonopodis pv. citri as a nitrogen source in defined medium significantly increases the production of xanthan gum. This increase is dependent on the L-glutamate concentration. In addition, we have also characterized a glutamate transport system that is dependent on a proton gradient and on ATP and is modulated by amino acids that are structurally related to glutamate. This is the first biochemical characterization of an energy substrate transport system observed in a bacterial phytopathogen with a broad economic and industrial impact due to xanthan gum production.
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Affiliation(s)
- Robert Rojas
- Department of Microbiology, Biomedical Sciences Institute, University of São Paulo, Avenida Lineu Prestes 1374, Cidade Universitária, São Paulo, 05508-900, Brazil,
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41
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Allosteric modulation of an excitatory amino acid transporter: the subtype-selective inhibitor UCPH-101 exerts sustained inhibition of EAAT1 through an intramonomeric site in the trimerization domain. J Neurosci 2013; 33:1068-87. [PMID: 23325245 DOI: 10.1523/jneurosci.3396-12.2013] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
In the present study, the mechanism of action and molecular basis for the activity of the first class of selective inhibitors of the human excitatory amino acid transporter subtype 1 (EAAT1) and its rodent ortholog GLAST are elucidated. The previously reported specificity of UCPH-101 and UCPH-102 for EAAT1 over EAAT2 and EAAT3 is demonstrated to extend to the EAAT4 and EAAT5 subtypes as well. Interestingly, brief exposure to UCPH-101 induces a long-lasting inactive state of EAAT1, whereas the inhibition exerted by closely related analogs is substantially more reversible in nature. In agreement with this, the kinetic properties of UCPH-101 unblocking of the transporter are considerably slower than those of UCPH-102. UCPH-101 exhibits noncompetitive inhibition of EAAT1, and its binding site in GLAST has been delineated in an elaborate mutagenesis study. Substitutions of several residues in TM3, TM4c, and TM7a of GLAST have detrimental effects on the inhibitory potency and/or efficacy of UCPH-101 while not affecting the pharmacological properties of (S)-glutamate or the competitive EAAT inhibitor TBOA significantly. Hence, UCPH-101 is proposed to target a predominantly hydrophobic crevice in the "trimerization domain" of the GLAST monomer, and the inhibitor is demonstrated to inhibit the uptake through the monomer that it binds to exclusively and not to affect substrate translocation through the other monomers in the GLAST trimer. The allosteric mode of UCPH-101 inhibition underlines the functional importance of the trimerization domain of the EAAT and demonstrates the feasibility of modulating transporter function through ligand binding to regions distant from its "transport domain."
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42
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Jaehme M, Michel H. Evaluation of cell-free protein synthesis for the crystallization of membrane proteins--a case study on a member of the glutamate transporter family from Staphylothermus marinus. FEBS J 2013; 280:1112-25. [PMID: 23279902 DOI: 10.1111/febs.12105] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2012] [Revised: 12/07/2012] [Accepted: 12/18/2012] [Indexed: 12/25/2022]
Abstract
Cell-free in vitro synthesis of proteins using coupled transcription/translation is considered to be a powerful alternative to the use of traditional cell-based expression systems. Recently, promising developments have been reported applying cell-free production to membrane proteins for structural biology and in particular for NMR spectroscopy. However, the general applicability of this system to produce large amounts of stable, functional and homogeneous membrane proteins as required for X-ray crystallography remains to be determined. Here, we present a systematic study comparing structural and functional properties of membrane proteins produced using Escherichia coli derived in vitro and in vivo expression systems. The function of the target membrane protein, a previously uncharacterized bacterial glutamate transporter homolog from Staphylothermus marinus, was analyzed using ligand binding and transport assays. In addition, the protein structure was investigated with respect to its overall fold and oligomeric state in different detergents. We found that the protein synthesized in vitro is highly stable and monodisperse. However, in contrast to the protein produced using an in vivo system, it was not able to assemble into the native trimeric state nor to bind substrate. We thus conclude that cell-free expression systems can compromise folding and function of such complex secondary active transporters. The expression product has to be carefully characterized prior to biophysical investigations like crystallography of membrane proteins.
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Affiliation(s)
- Michael Jaehme
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
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43
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Conformational ensemble of the sodium-coupled aspartate transporter. Nat Struct Mol Biol 2013; 20:215-21. [PMID: 23334289 PMCID: PMC3565060 DOI: 10.1038/nsmb.2494] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Accepted: 12/17/2012] [Indexed: 01/03/2023]
Abstract
Sodium and aspartate symporter from Pyrococcus horikoshii, GltPh, is a homologue of the mammalian glutamate transporters, homotrimeric integral membrane proteins controlling the neurotransmitter levels in brain synapses. These transporters function by alternating between outward and inward facing states, in which the substrate binding site is oriented toward the extracellular space and the cytoplasm, respectively. Here we employ double electron-electron resonance (DEER) spectroscopy to probe the structure and the state distribution of the subunits in the trimer within distinct hydrophobic environments of detergent micelles and lipid bilayers. Our experiments reveal a conformational ensemble of protomers sampling the outward and inward facing states with nearly equal probabilities, indicative of comparable energies, and independently of each other. On average, the distributions vary only modestly in detergent and in bilayers, but in several mutants unique conformations are stabilized by the latter.
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44
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Stolzenberg S, Khelashvili G, Weinstein H. Structural intermediates in a model of the substrate translocation path of the bacterial glutamate transporter homologue GltPh. J Phys Chem B 2012; 116:5372-83. [PMID: 22494242 PMCID: PMC3350225 DOI: 10.1021/jp301726s] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 04/10/2012] [Indexed: 01/05/2023]
Abstract
Excitatory amino acid transporters (EAATs) are membrane proteins responsible for reuptake of glutamate from the synaptic cleft to terminate neurotransmission and help prevent neurotoxically high, extracellular glutamate concentrations. Important structural information about these proteins emerged from crystal structures of GltPh, a bacterial homologue of EAATs, in conformations facing outward and inward. These remarkably different conformations are considered to be end points of the substrate translocation path (STP), suggesting that the transport mechanism involves major conformational rearrangements that remain uncharted. To investigate possible steps in the structural transitions of the STP between the two end-point conformations, we applied a combination of computational modeling methods (motion planning, molecular dynamics simulations, and mixed elastic network models). We found that the conformational changes in the transition involve mainly the repositioning the "transport domain" and the "trimerization domain" identified previously in the crystal structures. The two domains move in opposite directions along the membrane normal, and the transport domain also tilts by ∼17° with respect to this axis. Moreover, the TM3-4 loop undergoes a flexible, "restraining bar"-like conformational change with respect to the transport domain. As a consequence of these conformational rearrangements along the transition path we calculated a significant decrease of nearly 20% in the area of the transport-to-trimerization domain interface (TTDI). Water penetrates parts of the TTDI in the modeled intermediates but very much less in the end-point conformations. We show that these characteristics of the modeled intermediate states agree with experimental results from residue-accessibility studies in individual monomers and identify specific residues that can be used to test the proposed STP. Moreover, MD simulations of complete GltPh trimers constructed from initially identical monomer intermediates suggest that asymmetry can appear in the trimer, consonant with available experimental data showing independent transport kinetics by individual monomers in the trimers.
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Affiliation(s)
- Sebastian Stolzenberg
- Department of Physiology and
Biophysics, Weill Cornell Medical College, Cornell University, 1300 York Avenue, New York, New York 10065, United States
- Department of Physics, Cornell University, 109 Clark Hall, Ithaca, New York
14853-2501, United States
| | - George Khelashvili
- Department of Physiology and
Biophysics, Weill Cornell Medical College, Cornell University, 1300 York Avenue, New York, New York 10065, United States
| | - Harel Weinstein
- Department of Physiology and
Biophysics, Weill Cornell Medical College, Cornell University, 1300 York Avenue, New York, New York 10065, United States
- HRH Prince Alwaleed Bin Talal
Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill
Cornell Medical College, Cornell University, New York, New York 10065, United States
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45
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Hippocampal glutamate transporter 1 (GLT-1) complex levels are paralleling memory training in the Multiple T-maze in C57BL/6J mice. Brain Struct Funct 2011; 217:363-78. [PMID: 22113856 DOI: 10.1007/s00429-011-0362-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 11/08/2011] [Indexed: 12/25/2022]
Abstract
The glutamate transporter 1 (GLT-1) is essential for glutamate uptake in the brain and associated with various psychiatric and neurological disorders. Pharmacological inhibition of GLT-1 results in memory deficits, but no study linking native GLT-1 complexes was published so far. It was therefore the aim of the study to associate this highly hydrophobic, eight transmembrane spanning domains containing transporter to memory training in the Multiple T-maze (MTM). C57BL/6J mice were used for the spatial memory training experiments, and trained mice were compared to untrained (yoked) animals. Mouse hippocampi were dissected out 6 h after training on day 4, and a total enriched membrane fraction was prepared by ultracentrifugation. Membrane proteins were separated by blue native polyacrylamide gel electrophoresis (BN-PAGE) with subsequent Western blotting against GLT-1 on these native gels. Moreover, GLT-1 complexes were identified by mass spectrometry (nano-LC-ESI-MS/MS). Animals learned the MTM task and multiple GLT-1 complexes were detected at apparent molecular weights of 242, 480 and 720 kDa on BN-PAGE Western blotting. GLT-1 complex levels were significantly higher in the trained group as compared to yoked controls, and antibody specificity was verified by immunoblotting on multidimensional gels. Hippocampal GLT-1 was unambiguously identified by mass spectrometry with high sequence coverage, and glycosylation was observed. It is revealed that increased GLT-1 complex levels are paralleling and are linked to spatial memory training. We provide evidence that signal termination, represented by the excitatory amino acid transporter GLT-1 complexes, is involved in spatial memory mechanisms.
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46
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Miranda-Laferte E, Gonzalez-Gutierrez G, Schmidt S, Zeug A, Ponimaskin EG, Neely A, Hidalgo P. Homodimerization of the Src homology 3 domain of the calcium channel β-subunit drives dynamin-dependent endocytosis. J Biol Chem 2011; 286:22203-10. [PMID: 21502319 DOI: 10.1074/jbc.m110.201871] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Voltage-dependent calcium channels constitute the main entry pathway for calcium into excitable cells. They are heteromultimers formed by an α(1) pore-forming subunit (Ca(V)α(1)) and accessory subunits. To achieve a precise coordination of calcium signals, the expression and activity of these channels is tightly controlled. The accessory β-subunit (Ca(V)β), a membrane associated guanylate kinase containing one guanylate kinase (β-GK) and one Src homology 3 (β-SH3) domain, has antagonistic effects on calcium currents by regulating different aspects of channel function. Although β-GK binds to a conserved site within the α(1)-pore-forming subunit and facilitates channel opening, β-SH3 binds to dynamin and promotes endocytosis. Here, we investigated the molecular switch underlying the functional duality of this modular protein. We show that β-SH3 homodimerizes through a single disulfide bond. Substitution of the only cysteine residue abolishes dimerization and impairs internalization of L-type Ca(V)1.2 channels expressed in Xenopus oocytes while preserving dynamin binding. Covalent linkage of the β-SH3 dimerization-deficient mutant yields a concatamer that binds to dynamin and restores endocytosis. Moreover, using FRET analysis, we show in living cells that Ca(V)β form oligomers and that this interaction is reduced by Ca(V)α(1). Association of Ca(V)β with a polypeptide encoding the binding motif in Ca(V)α(1) inhibited endocytosis. Together, these findings reveal that β-SH3 dimerization is crucial for endocytosis and suggest that channel activation and internalization are two mutually exclusive functions of Ca(V)β. We propose that a change in the oligomeric state of Ca(V)β is the functional switch between channel activator and channel internalizer.
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Affiliation(s)
- Erick Miranda-Laferte
- Institut für Neurophysiologie, Medizinische Hochschule Hannover, 30625 Hannover, Germany
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Aoyama K, Watabe M, Nakaki T. Modulation of neuronal glutathione synthesis by EAAC1 and its interacting protein GTRAP3-18. Amino Acids 2011; 42:163-9. [PMID: 21373771 DOI: 10.1007/s00726-011-0861-y] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2010] [Accepted: 02/17/2011] [Indexed: 01/17/2023]
Abstract
Glutathione (GSH) plays essential roles in different processes such as antioxidant defenses, cell signaling, cell proliferation, and apoptosis in the central nervous system. GSH is a tripeptide composed of glutamate, cysteine, and glycine. The concentration of cysteine in neurons is much lower than that of glutamate or glycine, so that cysteine is the rate-limiting substrate for neuronal GSH synthesis. Most neuronal cysteine uptake is mediated through the neuronal sodium-dependent glutamate transporter, known as excitatory amino acid carrier 1 (EAAC1). Glutamate transporters are vulnerable to oxidative stress and EAAC1 dysfunction impairs neuronal GSH synthesis by reducing cysteine uptake. This may start a vicious circle leading to neurodegeneration. Intracellular signaling molecules functionally regulate EAAC1. Glutamate transporter-associated protein 3-18 (GTRAP3-18) activation down-regulates EAAC1 function. Here, we focused on the interaction between EAAC1 and GTRAP3-18 at the plasma membrane to investigate their effects on neuronal GSH synthesis. Increased level of GTRAP3-18 protein induced a decrease in GSH level and, thereby, increased the vulnerability to oxidative stress, while decreased level of GTRAP3-18 protein induced an increase in GSH level in vitro. We also confirmed these results in vivo. Our studies demonstrate that GTRAP3-18 regulates neuronal GSH level by controlling the EAAC1-mediated uptake of cysteine.
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Affiliation(s)
- Koji Aoyama
- Department of Pharmacology, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi, Tokyo, 173-8605, Japan
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48
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Nothmann D, Leinenweber A, Torres-Salazar D, Kovermann P, Hotzy J, Gameiro A, Grewer C, Fahlke C. Hetero-oligomerization of neuronal glutamate transporters. J Biol Chem 2010; 286:3935-43. [PMID: 21127051 DOI: 10.1074/jbc.m110.187492] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Excitatory amino acid transporters (EAATs) mediate the uptake of glutamate into neuronal and glial cells of the mammalian central nervous system. Two transporters expressed primarily in glia, EAAT1 and EAAT2, are crucial for glutamate homeostasis in the adult mammalian brain. Three neuronal transporters (EAAT3, EAAT4, and EAAT5) appear to have additional functions in regulating and processing cellular excitability. EAATs are assembled as trimers, and the existence of multiple isoforms raises the question of whether certain isoforms can form hetero-oligomers. Co-expression and pulldown experiments of various glutamate transporters showed that EAAT3 and EAAT4, but neither EAAT1 and EAAT2, nor EAAT2 and EAAT3 are capable of co-assembling into heterotrimers. To study the functional consequences of hetero-oligomerization, we co-expressed EAAT3 and the serine-dependent mutant R501C EAAT4 in HEK293 cells and Xenopus laevis oocytes and studied glutamate/serine transport and anion conduction using electrophysiological methods. Individual subunits transport glutamate independently of each other. Apparent substrate affinities are not affected by hetero-oligomerization. However, polarized localization in Madin-Darby canine kidney cells was different for homo- and hetero-oligomers. EAAT3 inserts exclusively into apical membranes of Madin-Darby canine kidney cells when expressed alone. Co-expression with EAAT4 results in additional appearance of basolateral EAAT3. Our results demonstrate the existence of heterotrimeric glutamate transporters and provide novel information about the physiological impact of EAAT oligomerization.
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Affiliation(s)
- Doreen Nothmann
- Institut für Neurophysiologie, Medizinische Hochschule Hannover, D-30625 Hannover, Germany
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Fallah G, Römer T, Detro-Dassen S, Braam U, Markwardt F, Schmalzing G. TMEM16A(a)/anoctamin-1 shares a homodimeric architecture with CLC chloride channels. Mol Cell Proteomics 2010; 10:M110.004697. [PMID: 20974900 PMCID: PMC3033684 DOI: 10.1074/mcp.m110.004697] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
TMEM16A/anoctamin-1 has been identified as a protein with the classic properties of a Ca(2+)-activated chloride channel. Here, we used blue native polyacrylamide gel electrophoresis (BN-PAGE) and chemical cross-linking to assess the quaternary structure of the mouse TMEM16A(a) and TMEM16A(ac) splice variants as well as a genetically concatenated TMEM16A(a) homodimer. The constructs carried hexahistidyl (His) tags to allow for their purification using a nondenaturing metal affinity resin. Neither His-tagging nor head-to-tail concatenation of two copies of TMEM16A(a) noticeably affected Ca(2+)-induced measured macroscopic Cl(-) currents compared with the wild-type TMEM16A(a) channel. The digitonin-solubilized, nondenatured TMEM16A(a) protein migrated in the BN-PAGE gel as a homodimer, as judged by comparison with the concatenated TMEM16A(a) homodimer and channel proteins of known oligomeric structures (e.g. the voltage-gated Cl(-) channel CLC-1). Cross-linking with glutaraldehyde corroborated the homodimeric structure of TMEM16A(a). The TMEM16A(a) homodimer detected in Xenopus laevis oocytes and HEK 293 cells dissociated into monomers following denaturation with SDS, and reducing versus nonreducing SDS-PAGE provided no evidence for the presence of intersubunit disulfide bonds. Together, our data demonstrate that the Ca(2+)-activated chloride channel member TMEM16A shares an obligate homodimeric architecture with the hCLC-1 channel.
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Affiliation(s)
- Ghada Fallah
- Molecular Pharmacology, RWTH Aachen University, Aachen, Germany
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50
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New views of glutamate transporter structure and function: advances and challenges. Neuropharmacology 2010; 60:172-81. [PMID: 20708631 DOI: 10.1016/j.neuropharm.2010.07.019] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Revised: 07/14/2010] [Accepted: 07/25/2010] [Indexed: 12/18/2022]
Abstract
Neuronal and glial glutamate transporters limit the action of excitatory amino acids after their release during synaptic transmission. Recent structural and functional investigations have revealed much about the transport and conducting mechanisms of members of the sodium-coupled symporter family responsible for glutamate clearance in the nervous system. In this review we summarize emerging views on the general structure, binding sites for substrates and coupled ions, and transport mechanisms of mammalian glutamate transporters, integrating results from a large body of work on carrier structure-function relationships with several crystal structures obtained for the archaeal ortholog, Glt(Ph).
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